Reports
Placement, consolidation, and erosion studies at open-water placement Site 92, 2005-2006 (Year 8)
2007, Offerman, K.A., and Panageotou, W.
File Reports, Coastal and Estuarine Geology, File Report 2007-01
Executive Summary
The eighth year (Year 8) of dredged sediment placement at Site 92 occurred between October 2, 2005 and December 10, 2005. A clamshell-bucket dredge excavated approximately 0.78 million cubic yards (mcy) of clayey-silt sediment from the Chesapeake & Delaware (C&D) Canal approach channel. The sediment was placed via bottom-release scows into a designated drop zone in the northern portion of Site 92. Placement occurred in water depths that ranged from −16 to −23 feet MLLW.
The volume of placed sediment identified by Maryland Geological Survey (MGS) at the completion of placement was 0.53 ± 0.10 mcy. This represented a mean volumetric deficit of 0.25 mcy, or 31.7%. The total area covered by placed sediment was 0.87 million square yards, or approximately 180.7 acres. The majority of the deposit was 0.3 to 8 ft thick with a maximum thickness of 8.8 feet.
The placed sediments underwent elevation, volumetric, and sediment mass changes during the following nine months. The maximum thickness of the placed sediments decreased by 3.4 ft, from 8.8 ft at completion of placement to 5.4 ft at nine months. There was a 0.9% volumetric reduction at one month, 12.4% at three months, 20.9% at six months, and 38.5% at nine months following placement. It was estimated that approximately one-quarter of the volumetric change resulted from consolidation and three-quarters from erosion. During the combined placement and post-placement periods, there was approximately a 53% loss of sediment mass (-196,134 tons) at Site 92.
Year 8 placement utilized 0.33 mcy, or approximately 5%, of the site volume capacity. To date, dredged sediment placement used approximately 51% of the total site volume capacity, and 49% is available for future placements.
